1). Field of the Invention
This invention relates to a no-flow underfill material.
2). Discussion of Related Art
A semiconductor package may be constructed from a package substrate having bond pads thereon and an integrated circuit die having bumps formed thereon. A fluxing agent is usually deposited over the package substrate and the bond pads and the bumps are then brought into contact with the bond pads. Subsequent heating in a reflow oven attaches the bumps to the bond pads. The fluxing agent removes oxides from surfaces of the bond pads and bumps to ensure a reliable joint between the bumps and the bond pads.
The fluxing agent is subsequently washed out in a defluxing machine. An underfill material is then dispensed next to the die on the substrate utilizing a dispensing machine. The underfill material then flows under capillary action into and fills a gap between the die and the substrate, with or without the help of heating. The underfill material serves to redistribute stresses on the bumps due to a mismatch in a coefficient of thermal expansion (CTE) of the substrate and a CTE of the die when the package is heated or cooled.
A so-called no-flow underfill material may be used instead of a conventional fluxing agent to eliminate the need for a defluxing machine and other machinery, and to significantly reduce throughput time. A no-flow underfill material is applied like a conventional fluxing agent and to an extent serves the purpose of a conventional fluxing agent. The no-flow underfill material cures while the package is transferred through a reflow oven, and, to an extent, can then serve the additional purpose of a conventional underfill material. Post cure of the material may be needed.
Existing no-flow underfill materials have been shown to be unsatisfactory because of one or more reasons such as a very high CTE, high moisture absorption, etc.